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Sidestepping Galileo's jammed antenna.

After several failed attempts to free Galileo's stuck main antenna, scientists last week revealed their plant for continuing the spacecraft's mission to Jupiter without it.

The main antenna, which resembles a large umbrella, failed to open in April 1991 after two of its ribs jammed. Since then, scientists have used Galileo's two smaller, low-gain antennas to transmit data to Earth. While this antennas have performed well so far, schientists worried that when Galileo begins orbiting Jupiter in 1995, the craft's experiments would flood the antennas with more data than they could handle.

Now NASA officials say that a few high-tech tricks could soup up Galileo's communication system to handle much of the data. "The good news we have today is that we have found a way to accomplish the majority of the orbiter's objectives," Galileo project manager WilliamJ J. O'Neill of NASA said at a press conference last week. In fact, Galileo could still complete up to 70 percent of its experiments without the main antenna, mission scientists say.

Researchers plan to boost the performance of the smaller antennas in two ways. First, Galileo's on-board computer would be reprogrammed to squeeze data into fewer computer bits, enabling scientists to send back more images and sensor information. Second, researchers plan to make the network of ground antennas that receive Galileo's signals more sensitive. Galileo's low-gain antennas could then step up data transmission from 10 bits per second to 100 bits per second. Together, these modifications shouls improve Galileo's present capabilities a hundredfold.

Loss of the main antenna would still hurt some experiments, especially those that rely on numerous high-resolution pictures, says Galileo project scientist Torrence V. Johnson. Galileo could complete about 80 percent of its atmospheric research, 60 percent of its magnetosphere experiments and 70 percent of its studies of Jupiter's moons, he adds.

Scientists haven't abandonned the idea of unfurling the main antenna. They will make another attempt in December, when the spacecraft whips around Earth for its final gravitional assist on the way to Jupiter.

But even if future efforts to free the antenna fail, scientists remain confident of Galileo's success. "We can still do a very good job," O'Neil says.
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Title Annotation:Galileo spacecraft's smaller antennas to be boosted
Author:Stroh, Michael
Publication:Science News
Article Type:Brief Article
Date:Jun 20, 1992
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